ABSTRACT: During the funding of the current R-01, our team made 4 discoveries related to human and mouse somatostatin receptor subtype five (hSSTR5, mSSTR5) and pancreatic duodenal homeobox-1 (PDX-1) that are highly translatable for patients suffering with islet neoplasia (INeo): 1. our SSTR5-/- mice develop INeo associated with hyperinsulinemia, hypoglycemia and PDX-1 overexpression, suggesting mSSTR5 regulates both insulin secretion and INeo via PDX-1;2. PDX-1 regulates INeo cell proliferation and iv PDX-1 shRNA therapy prevents hypoglycemic death in a metastatic insulinoma mouse model, suggesting PDX-1 is a molecular target for INeo;3. we found a germline hSSTR5 SNP with a proline to leucine substitution at C terminal position 335 (hSSTR5 P335L) in ~50% of human INeo tumors. Preliminary in vitro data reveal that hSSTR5 P335L is hypofunctional resulting in PDX-1 overexpression and lack of response to SSTR5 analogue PRL-1980 in INeo cells, suggesting genomic hSSTR5 variation predicts response to therapy;4. our rat insulin promoter-thymidine kinase (RIP-TK) vector, which is activated by PDX-1, and F18-FHBG prodrug can be used to image PDX-1 expression in INeo tumors in mice and could be used to track response to therapy. Hypotheses: a) hSSTR5 regulates insulin and INeo via PDX-1, b) hSSTR5 P335L is a hypofunctional receptor with altered PDX-1 regulation of INeo, and c) genomic variation of hSSTR5 and variations in expression of hSSTR5, hSSTR5 P335L and PDX-1 predict response to targeted therapies. Specific Aim 1: to determine whether a) distribution of hSSTR5 genomic variation in INeo patients can be validated using TaqMan Allelic Discrimination assay and b) variations in expression of hSSTR5, hSSTR5 P335L and/or PDX-1 of INeo specimens can be validated using QPCR, Western blot and Quantum Dot (Q Dot) deconvolution imaging and image analysis. Specific aim 2: to determine whether a) hSSTR5 regulates insulin and INeo cell proliferation via PDX-1, b) hSSTR5 P335L is a hypofunctional receptor with altered PDX-1 regulation of INeo, and c) hSSTR5 genomic variation and variations in hSSTR5, hSSTR5 P335L and PDX-1 expression levels predict response to SSTR5-specific analogue PRL-1980 vs PDX-1 shRNA therapies in i) &#946;TC-6hSSTR5 SCID mouse model, ii) &#946;TC-6hSSTR5 P335L SCID mouse model, iii) &#946;TC-6SSTR5KD (Knock Down) SCID mouse model, iv) hSSTR5 knock-in mice, v) hSSTR5 P335L knock-in mice and vi) SSTR5-/- mice. Specific Aim 3: to determine whether a) imaging agents to detect PDX-1 expression using rat insulin promoter-thymidine kinase (RIP-TK) in INeo mouse models from aim 2 can be validated using 18F-FHBG for microPET imaging and/or dual labeled analogues for optical imaging and tomography, b) the response to targeted therapies can be studied using RIP-TK/ 18F-FHBG microPET imaging and is dependent upon PDX-1 expression levels and c) microPET PRL- 1980-Cu64 imaging can differentiate between SSTR5 positive and SSTR5 negative INeo tumors and will confirm the role of PDX-1 in therapeutic response in vivo.